This invention relates to screening machines of the type used to separate or classify mixtures of solid particles of different sizes. The invention also relates to screening machines of the type used for liquid/solid separations, i.e., for separating solid particles of specific sizes from a liquid in which they are carried. More particularly, the invention relates to a mechanism and method for sealing components within the screening machine.
In screening machines of the type described, a screen (which may be woven, an aperture plate or another design) is mounted in what is often called a "screen frame" or "screen deck" which includes a supporting peripheral frame around the perimeter of the screen. Typically associated with this screen frame are other material handling elements which are moved with the screen frame and form walls or partitions above or below the screen frame for containing the liquid and/or particulate materials adjacent to the screen and directing them to appropriate outlets. These elements may comprise a top cover and a pan beneath the screen frame. In the case of screening machines with multiple screens or deck units, spacer pans or frames are provided between the multiple screens.
The screen frames are often removed from the screening machines for cleaning, replacement, readjustment or installation of a screen of a different mesh size or the like. The screen frame is releasably mounted to a carrier, frame, table or box to which vibratory motion is imparted, typically by one or more eccentric motors or other means of excitation. The carrier, frame, table or box is referred to herein as a "vibratory carrier". The vibratory carrier may be moved in oscillatory, vibratory, gyratory, gyratory reciprocating, fully gyratory, rotary or another type of motion or combinations thereof, all of which are herein collectively referred to as "vibratory" motion or variations of that term.
In large commercial screening machines, the weight of the various components including the screen assembly carried by the vibratory carrier, and the weight of the material being processed on the screen assembly may total several hundred pounds or more. This presents a very substantial inertial mass which resists the changes of motion applied thereto by the vibratory drive acting through the vibratory carrier. As a result of these inertial forces, a relative motion may exist between the vibratory carrier and the screen frame. Typically, the screen frame and vibratory carrier are each constructed of metal which could result in significant noise, wear or damage due to the relative motion or rubbing action therebetween. The resulting impact forces between the screen frame and vibratory carrier significantly increase the stresses on the components and reduce their useful life.
Reducing the metal-to-metal contact minimizes the wear on the various metal components and the noise associated with the operation of the screening machine. In some screening machines, a seal is provided between the screen frame and adjacent components such as other screen frames or the vibratory carrier. The seal prevents the escape of material from the screen frame and reduces the detrimental metal-to-metal contact between the screen frame and adjacent components. Currently, certain screen frame designs may not be sealed or secured relative to the remainder of the screening machine, particularly in larger screening machines. This results in the above-described metal-to-metal contact between the screen frame and the remainder of the screening machine and prevents the screening of very fine material, such as sand or the like. The screen frames in larger screening machines are typically inserted and/or removed from the machine in a generally horizontal direction typically through an opening or slot at the head or foot end of the machine or on the side of the machine. This method of installation and removal of the screen frame is detrimental to known sealing arrangements because a seal which would engage the screen frame could be torn or damaged during the installation/removal of the screen frame. In other screening machines, the screen frame is inserted vertically, typically from the top of the machine.
One known sealing mechanism for screening machines is disclosed in U.S. Pat. No. 5,226,546 which relates to a pneumatic seal that is inflated to raise up the screen frame for engagement with a seal. However, pneumatic systems such as those shown in the identified patent often leak thereby lowering the seal pressure. Furthermore, pneumatic systems require an air source at the machine location and traditionally are only used with the insertion/removal of the screen frame through the top of the machine in a generally vertical direction. Furthermore, screening machines with multiple screens and screen frames may require many or all of the screen frames to be removed for access to an individual screen frame. Furthermore, inspection of the resulting seal in pneumatic systems is not readily available.
Known alternatives to pneumatic sealing systems for screening machines include mechanical clamps or locks located at a number of spaced locations on the sides of the machine. One example of this type of known mechanism is disclosed in U.S. Pat. No. 5,392,925. However, to clamp each of the screens in place, the user must progressively move along a first side of the machine tightening and adjusting each of the individual mechanism and then proceed to the opposite side of the machine and repeat the same procedure. This mode of operation is inefficient, time consuming and inconvenient for the user. Additionally, the user can not easily inspect the resulting seal when going from clamp site to clamp site in such systems. Furthermore, the screen frames utilized in screening machines with known mechanical sealing mechanisms must be robust and heavy because they are supported at individual spaced locations by the clamps.
Therefore, it is apparent that there is a need for a sealing mechanism and method for screening machines which avoids metal-to-metal contact between the screen frame and adjacent components of the screening machine without the disadvantages associated with known pneumatic or mechanical sealing systems.